A method of producing a three-dimensional photonic crystal by laminating a layer having a periodic structure, the method including the steps of forming a first structure and a second structure each including the layer having the periodic structure; and bonding a first bonding layer of the first structure and a second bonding layer of the second structure. The first bonding layer is one layer obtained by dividing a layer constituting the three-dimensional photonic crystal at a cross section perpendicular to a lamination direction, and the second bonding layer is the other layer obtained by dividing the layer constituting the three-dimensional photonic crystal at the cross section perpendicular to the lamination direction.
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1. A method of producing a three-dimensional photonic crystal by laminating a layer having a periodic structure, the method comprising the steps of:
forming a first structure and a second structure each including the layer having the periodic structure; and
bonding a first bonding layer of the first structure and a second bonding layer of the second structure,
wherein the first bonding layer is one layer obtained by dividing a layer constituting the three-dimensional photonic crystal at a cross section perpendicular to a lamination direction, and the second bonding layer is the other layer obtained by dividing the layer constituting the three-dimensional photonic crystal at the cross section perpendicular to the lamination direction.
2. The method of producing a three-dimensional photonic crystal according to
3. The method of producing a three-dimensional photonic crystal according to
4. The method of producing a three-dimensional photonic crystal according to
5. The method of producing a three-dimensional photonic crystal according to
6. An optical functional device comprising a three-dimensional photonic crystal produced by the method according to
7. An optical functional device comprising a three-dimensional photonic crystal produced by the method according to
8. A light emitting device comprising the optical functional device according to
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1. Field of the Invention
The present invention relates to a method of producing a three-dimensional photonic crystal and an optical functional device using the three-dimensional photonic crystal.
2. Description of the Related Art
Yablonovitch has suggested in “Physical Review Letters, Vol. 58, pp. 2059, 1987” that characteristics of electromagnetic waves such as transmission and reflection can be controlled by periodically arranging structures each having a size less than or equal to the wavelength. Such a structure is known as a photonic crystal and can control the propagation of light. In particular, a three-dimensional photonic crystal having a three-dimensional fine periodic structure can three-dimensionally control the propagation of light and thus can be applied to various applications such as a mirror with a reflectivity of 100% independent of the angle of incident light.
A woodpile structure is known as a crystal structure of such a three-dimensional photonic crystal. A structure formed by laminating a plurality of layers each having a periodic structure (layer-by-layer (LBL) structure) like the woodpile structure can be produced by semiconductor process technology (see Japanese Patent Application Laid-Open No. 2001-281473, U.S. Pat. No. 5,998,298, Japanese Patent No. 03721815, U.S. Pat. Nos. 6,650,672, and 6,479,371). Japanese Patent Application Laid-Open No. 2001-281473 and U.S. Pat. No. 5,998,298 propose a method of producing a three-dimensional photonic crystal by sequentially laminating a plurality of layers. In addition, Japanese Patent No. 03721815, U.S. Pat. Nos. 6,650,672 and 6,479,371 propose a method of producing a three-dimensional photonic crystal by bonding a plurality of layers.
A photonic band gap is caused by a crystal structure whose permittivity changes periodically. Therefore, production of a photonic crystal which exhibits a photonic band gap in a desired wavelength band requires formation of a crystal structure having an accurate period in a three-dimensional direction. Moreover, in order to produce a three-dimensional photonic crystal by laminating a plurality of layers having a periodic structure, the plurality of layers having a periodic structure is required to be strongly bonded together.
Unfortunately, the production methods of Japanese Patent Application Laid-Open No. 2001-281473 and U.S. Pat. No. 5,998,298 includes many steps since layers are laminated layer by layer. Note that the production methods of Japanese Patent No. 03721815, U.S. Pat. Nos. 6,650,672 and 6,479,371 can reduce the number of steps since structures having a plurality of layers are bonded together. However, since the bond strength of a structure is proportional to the bonding area thereof, it is difficult to increase the bond strength by bonding parts of periodic structure different from each other.
An object of the present invention is to produce a three-dimensional photonic crystal having a strong bond strength with fewer production steps, and to provide an optical functional device using the three-dimensional photonic crystal. In an aspect of the present invention, there is provided a method of producing a three-dimensional photonic crystal by laminating a layer having a periodic structure, the method comprising the steps of forming a first structure and a second structure each including the layer having the periodic structure; and bonding a first bonding layer of the first structure and a second bonding layer of the second structure, wherein the first bonding layer is one layer obtained by dividing a layer constituting the three-dimensional photonic crystal at a cross section perpendicular to a lamination direction, and the second bonding layer is the other layer obtained by dividing the layer constituting the three-dimensional photonic crystal at the cross section perpendicular to the lamination direction.
In another aspect of the present invention, there is provided an optical functional device comprising a three-dimensional photonic crystal produced by the above-described method.
In still another aspect of the present invention, there is provided a light emitting device comprising the above-described optical functional device.
The present invention makes it possible to produce a three-dimensional photonic crystal having a strong bond strength with fewer production steps.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
FIGS. 2AZ, 2AX, 2BZ, 2BX, 2CZ, 2CX, 2D1, 2D2 2E and 2F are explanatory drawings illustrating a method of producing the three-dimensional photonic crystal of the first embodiment.
FIGS. 3A1, 3A2, 3B and 3C are explanatory drawings illustrating a conventional method of producing a three-dimensional photonic crystal.
FIGS. 5AZ, 5AX, 5BZ, 5BX, 5CZ, 5CX, 5D1, 5D2, 5E, 5F1 and 5F2 are explanatory drawings illustrating a method of producing the three-dimensional photonic crystal of the second embodiment.
FIGS. 6A1, 6A2, 6A3, 6A4, 6B, 6C and 6D are explanatory drawings illustrating a plurality of bonding steps of a third embodiment.
FIGS. 8A1, 8A2, 8B, 8C, 8CP, 8D, 8E and 8F are explanatory drawings illustrating an alignment method of a fourth embodiment.
Preferred embodiments of the present invention will now be described in detail in accordance with the accompanying drawings.
Note that throughout the drawings, like reference numerals or characters refer to like components. The method of producing the three-dimensional photonic crystal of the present invention includes a structure producing step and a bonding step. The structure producing step includes forming a first structure and a second structure each having a layer with a periodic structure. The first structure has a first bonding layer on an outermost surface layer thereof; and the first bonding layer is one layer obtained by dividing a layer of the three-dimensional photonic crystal along the lamination direction.
The outermost surface layer of the first structure has the first bonding layer which is one layer obtained by dividing one layer constituting the three-dimensional photonic crystal at a cross section perpendicular to the lamination direction. The outermost surface layer of the second structure has the second bonding layer which is the other layer obtained by dividing the one layer constituting the three-dimensional photonic crystal at the cross section perpendicular to the lamination direction. In the bonding step, the first bonding layer of the first structure is bonded to the second bonding layer of the second structure. The periodic structure of the first bonding layer matches with the periodic structure of the second bonding layer, and thus the both bonding layers are bonded together such that the respective periodic structures are overlapped to each other in the lamination direction. When the first bonding layer and the second bonding layer are bonded together, one layer of the three-dimensional photonic crystal is formed.
(First Embodiment)
The third layer 1003 has the same shape as the columnar structure 1001a and has a periodic structure in which a plurality of columnar structures (prisms) 1003a extending in the Y axis direction are arranged at the pitch P. The third layer 1003 is placed at a position shifted by P/2 in the X axis direction with respect to the columnar structure (prism) 1001a of the first layer 1001. The fourth layer 1004 has the same shape as the columnar structure 1002a and has a periodic structure in which a plurality of columnar structures (prisms) 1004a extending in the X axis direction are arranged at the pitch P. The fourth layer 1004 is placed at a position shifted by P/2 in the Y axis direction with respect to the columnar structure (prism) 1002a of the second layer 1002.
By referring to
As illustrated in
As described above, according to the steps of
Likewise, a structure 120 (second structure) constituting a part of the woodpile structure is produced by laminating the fourth layer 1004 and a layer 121 having a periodic structure constituting a part of the third layer 1003 (FIG. 2D2). The outermost surface layer of the second structure 120 has the other layer 121 obtained by dividing the third layer 1003 which is one layer of the three-dimensional photonic crystal 1000 at the cross section perpendicular to the lamination direction.
Here, the outermost surface layer 111 (first bonding layer) of the structure 110 and the outermost surface layer 121 (second bonding layer) of the structure 120 are produced such that the respective periodic structures are matched with each other. In the case of the woodpile structure, the columnar structures 101a to 104a having the same width W and height H in all layers are arranged at the same lattice constant P. In addition, the sum (H1+H2) of the height H1 of the first bonding layer 111 and the height H2 of the second bonding layer 121 is the same as the height H of the columnar structure of the woodpile structure.
Then, the structure 110 is bonded to the structure 120 such that the layer 111 faces the layer 121 (
According to the present embodiment, the first structure and the second structure each having a plurality of layers are bonded to each other. Therefore, the number of steps can be reduced in comparison with a production method in which layers are laminated one by one.
The bonding portion of the first bonding layer 111 and the second bonding layer 121 is a cross-over region of the columnar structures each having a width W. Thus, the bonding area (adhesive area) S is the square of W (W×W) (
Thus, the method of the present embodiment can produce a three-dimensional photonic crystal having a large bond strength with fewer producing steps. Note that according to the present embodiment, a woodpile structure is used as the three-dimensional photonic crystal, but any structure may be produced in the same manner as long as the structure is an LBL structure.
(Second Embodiment)
A second layer 2002, a fourth layer 2004, a sixth layer 2006 and an eighth layer 2008 each are an additional layer arranged such that the second layer 2002 is disposed between the first layer 2001 and the third layer 2003; the fourth layer 2004 is disposed between the third layer 2003 and the fifth layer 2005; the sixth layer 2006 is disposed between the fifth layer 2005 and the seventh layer 2007; and the eighth layer 2008 is disposed between the seventh layer 2007 and another first layer (a first layer of the next periodic structure). The additional layers 2002, 2004, 2006 and 2008 each have discrete structures 2002a, 2004a, 2006a and 2008a respectively at a position corresponding to a cross-over point of columnar structures.
According to the present embodiment, the three-dimensional photonic crystal has two layers 2001 and 2002 each having a different periodic structure as viewed from the lamination direction, but may be made of three or more kinds of periodic structures.
Like the first embodiment, the first bonding layer 111 and the second bonding layer 121 are formed such that the sum of the thicknesses becomes H. The first bonding layer 111 and the second bonding layer 121 are bonded together such that the respective periodic structures are overlapped. Then, a fifth layer 2005 having a columnar structure is formed (
That is, in order to increase the bond strength, it is preferable that the first bonding layer and the second bonding layer is set to one layer and the other layer respectively obtained by dividing a layer having the largest area of a structure constituting a periodic structure at a cross section perpendicular to the lamination direction of the three-dimensional photonic crystal. According to the present embodiment, a three-dimensional photonic crystal having a strong bond strength can be produced with respect to a three-dimensional photonic crystal having a plurality of periodic patterns. Note that according to the present embodiment, a structure illustrated in
(Third Embodiment)
Here, the structures 110, 120, 130 and 140 are produced such that each of the layer 111 just on the substrate 11 and the outermost surface layer 121 has a height of H/2. In addition, the production is performed such that the structure 110 and the structure 130 have the same shape; and the structure 120 and structure 140 have the same shape. Further, like the first embodiment, a structure 150 is produced by bonding the structure 110 and the structure 120; and a structure 160 is produced by bonding the structure 130 and the structure 140 (
According to the methods disclosed in Japanese Patent Application Laid-Open No. 2001-281473, U.S. Pat. No. 5,998,298 and Japanese Patent No. 03721815, woodpile layers 71 to 75 are bonded layer by layer as illustrated in
(Fourth Embodiment)
Specifically, a columnar structure of the first bonding layer 111 is selectively covered with a resist 104 using photolithography or the like (
According to the present embodiment, the sacrifice portion 111b is used for alignment when the structure 110 and the structure 120 are bonded to each other. More specifically, in the bonding step, the first bonding layer 111 and the second bonding layer 121 are bonded to each other by inserting the sacrifice portion of the first bonding layer 111 into the interspace of the structure 120 of the second bonding layer 121. In the step of
Like the first embodiment, semiconductor materials and dielectric materials are used as the materials of the three-dimensional photonic crystal. For example, when TiO2 is used, Cu may be used as the sacrifice portion 111b, PMMA may be used as the resist 2, and acetone may be used as the etchant. Subsequently, bonding is performed such that the layer 111 of the structure 110 in which the sacrifice portion 111b is formed faces the layer 121 of the structure 120. Since the height H3 of the sacrifice portion 111b is higher than the height H1 of the bonding layer 111, the bonding can be performed such that the columnar structure of the bonding layer 121 is overlapped to the columnar structure of the bonding layer 111 (
As described above, according to the present embodiment, in the bonding step, the bonding layer 111 of the structure 110 is bonded to the bonding layer 121 of the structure 120 using the sacrifice portion 111b for alignment. Subsequently, the sacrifice portion 111b is selectively removed. Then, the bonding layer 111 and the bonding layer 121 form one layer of the three-dimensional photonic crystal. Thus, the method of the present embodiment facilitates alignment in the bonding step.
(Fifth Embodiment)
(Sixth Embodiment)
A current injection type optical functional device using a three-dimensional photonic crystal will be described. The three-dimensional photonic crystal uses a woodpile structure, but another LBL structure may be used likewise. When an optical functional device operating by current injection is to be produced, there is a problem of carrier loss at a bonding surface of each layer of the three-dimensional photonic crystal.
According to the production method of the present invention, the first bonding layer 111 and the second bonding layer 121 are bonded to each other such that the respective periodic structures are overlapped to each other. Therefore, no dangling bond occurs and non-emission recombination can be reduced in comparison with a conventional method. In addition, the electrical resistance is proportional to the cross-sectional area of the current path. Thus, a resistance value in a portion having a small cross-sectional area becomes dominant. When bonding is performed conventionally such that the columnar structures are orthogonal to each other, the bonding area is relatively small and thus the resistance value becomes large as well as the resistance value is further increased due to contact failure on the bonding surface.
According to the present invention, the first bonding layer 111 and the second bonding layer 121 are bonded to each other such that the respective periodic structures are overlapped to each other, and thus the resistance value can be easily suppressed in comparison with a conventional method. In addition, the resistance value can be reduced by appropriately arranging a conductive material at least in a part of the first bonding layer 111 and the second bonding layer 121.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2009-094041, filed Apr. 8, 2009, which is hereby incorporated by reference herein in its entirety.
Tamamori, Kenji, Numata, Aihiko, Hoshi, Hikaru
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